Kids, who are born first or have had breech births or whose mothers are 35 or older at the time of birth, face a greater risk of developing an autism spectrum disorder, according to a new study.
Autism is a complex brain disorder that impairs social, communicative, and behavioural development and often is characterized by extreme behaviour.
Researchers at University of Utah School of Medicine have showed that women who give birth at 35 or older are 1.7 times more likely to have a child with an autism spectrum disorder (ASD), compared with women between the ages of 20-34.
Also, the researchers found that children diagnosed with ASD also were nearly 1.8 times more likely to be the firstborn child.
Although the researchers didn't identify a causal relationship between breech births and autism, children diagnosed with the disorder were more than twice as likely to have been a breech presentation-meaning they were not born head first.
"The results of this study give us an opportunity to look more closely at these risk factors for children across the autism spectrum, and not only those diagnosed with autism. This shows that further investigation of the influence of prenatal factors is warranted," said first author Deborah A. Bilder, M.D., assistant professor of psychiatry.
For the study, the researchers examined the birth records of Utah children who had been identified as having an autism spectrum disorder in a 2002 epidemiological study by the U.S. Centres for Disease Control and Prevention (CDC).
That study looked at 8-year-old children in Utah's three most populous counties-Salt Lake, Davis, and Utah-and used nationally accepted criteria for an ASD classification.
They then compared birth records for children identified with an ASD with unaffected children born in those three counties in 1994.
Of that group, 196 were identified with an ASD. Birth certificates were available for 132 of those children, and the researchers examined those records for possible prenatal, perinatal, and neonatal risk factors related to ASD. The investigation showed that the mother's age when giving birth (older than 34), breech presentation, and being firstborn were significant risk factors for the development of an ASD.
The researchers also identified a small but significant relationship between the increased duration of education among mothers of those children.
A possible explanation for the correlation of firstborn children might be that parents are reluctant to have a second child if the first is diagnosed with ASD. And increased risk associated with advanced maternal age could be because the changes in genes occurring over time may contribute to autism spectrum disorders.
The association found between breech presentation and ASD most likely indicates a shared cause, such as neuromuscular dysfunction. The vast majority of children born breech, however, are healthy.
The study has been published in the online issue of the journal Pediatrics.